How to ignore certain letters and spaces in character arrays - c++

Question

Trying to make an else statement that get rid of all other letter and spaces then the ones i want. This function is to change user inputted letters into other letters
using namespace std;
void dna_to_rna(char rna[])
{
for (int i = 0; i < 100; i++)
{
if (rna[i] == 'a' || rna[i] == 'A')
rna[i] = 'U';
else if (rna[i] == 'c' || rna[i] == 'C')
rna[i] = 'G';
else if (rna[i] == 'g' || rna[i] == 'G')
rna[i] = 'C';
else if (rna[i] == 't' || rna[i] == 'T')
rna[i] = 'A';
}
What should the else statement look like in order to drop all other chars?

Answer 1

If the input parameter can be changed to std::string, then you can use one of the following implementation:
void dna_to_rna(std::string& rna)
{
auto it = rna.begin();
while (it != rna.end())
{
if (*it == 'a' || *it == 'A') *it = 'U';
else if (*it == 'c' || *it == 'C') *it = 'G';
else if (*it == 'g' || *it == 'G') *it = 'C';
else if (*it == 't' || *it == 'T') *it = 'A';
else
{
it = rna.erase(it);
continue; // it already "points" to the next element
}
++it;
}
}
std::string dna_to_rna(const std::string& dna)
{
std::string rna;
for (auto c : dna)
{
if (c == 'a' || c == 'A') rna += 'U';
else if (c == 'c' || c == 'C') rna += 'G';
else if (c == 'g' || c == 'G') rna += 'C';
else if (c == 't' || c == 'T') rna += 'A';
}
return rna;
}

Answer 2

Maybe like this:
using namespace std;
void dna_to_rna(char rna[])
{
string s = "";
for (int i = 0; i < 100; i++)
{
if (rna[i] == 'a' || rna[i] == 'A')
s += 'U';
else if (rna[i] == 'c' || rna[i] == 'C')
s += 'G';
else if (rna[i] == 'g' || rna[i] == 'G')
s += 'C';
else if (rna[i] == 't' || rna[i] == 'T')
s += 'A';
}
strcpy(rna, s.c_str());
}
The idea is simply to use a std::string as a temporary buffer. The string is empty to start with. Then you add the characters you want one-by-one. When done with the loop, copy the content of the std::string back to the rna-array.

Answer 3

To make you code much simpler, and easier to read:
using namespace std;
void dna_to_rna(char rna[]) {
int arrLength = sizeof(rna)/sizeof(rna[0]); // Get size of array
for (int i = 0; i < arrLength; i++){
if (toupper(rna[i]) == 'A'){
rna[i] = 'U';
}
else if (toupper(rna[i]) == 'C') {
rna[i] = 'G';
}
else if (toupper(rna[i]) == 'G'){
rna[i] = 'C';
}
else if (toupper(rna[i]) == 'T'){
rna[i] = 'A';
}
}
}

Answer 4

I created a second array and as long as the information that I was looking for met the criteria that was necessary I placed it into the second array making sure that the position that I was placing it in the array was always in the right spot by creating a second variable that would count the the proper position in the array then just cout array
using namespace std;
void dna_to_rna(char rna[])
{
int x = 0;
char newrna[100];
for (int i = 0; i < 100; i++)
{
if (rna[i] == 'a' || rna[i] == 'A')
{
newrna[x] = 'U';
x++;
}
else if (rna[i] == 'c' || rna[i] == 'C')
{
newrna[x] = 'G';
x++;
}
else if (rna[i] == 'g' || rna[i] == 'G')
{
newrna[x] = 'C';
x++;
}
else if (rna[i] == 't' || rna[i] == 'T')
{
newrna[x] = 'A';
x++;
}
}